wrong macro expansion (multiple macros)

[danmar]

First reported in Cppcheck trac here:
https://trac.cppcheck.net/ticket/9538

Code:

#define at(x, y) x##y
#define b(...)                                                                 \
  aa(__VA_ARGS__, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,  \
     , , , , , , , , 2)
#define aa(c, d, a, b, e, f, g, h, ab, ac, i, ad, j, k, l, m, n, o, p, ae, q,  \
           r, s, t, u, v, w, x, y, z, af, ag, ah, ai, aj, ak, al, am, an, ao,  \
           ap)                                                                 \
  ap
#define aq(...) ar(b(__VA_ARGS__), __VA_ARGS__) static_assert(true, "")
#define ar(ap, ...) at(I_, ap)(__VA_ARGS__)
#define I_2(as, a)
aq(a, array);

simplecpp outputs I_2 ( a , array ) static_assert ( true , "" ) ; but gcc -E output is static_assert ( true , "" ) ;